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 Wandering firing points on HEI unit
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Bill Boyle
Horse Feathers (Charter Member)

USA
4793 Posts

Posted - 28 Apr 2014 :  10:20:27 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
I'm working on an HEI unit to recurve. However, I've noticed a malfunction that is so far unexplained.

One of the base line tests I perform on any distributor sent to me for recurving is to perform one basic test and that is to see how well it fires at a steady rpm. Pick an rpm. My SUN machine shows all 8 fire points and you can see how consistent it is. A good unit will have very little, if any movement across the testing rpm (800 to 6000+).

This particular unit is inconsistent and drifts away from each firing point--it just keeps going.

Why this is happening is the puzzling question. When I locked the advance so weights would have no effect on advancing the unit, that had no effect on it. The drift or wander continued.

The pick-up coil is a new one apparently installed by the owner. It appears to be one correct for Pontiac and is not one from another GM line.

Very puzzling.



"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.

67drake
Sitting Duck

Azerbaijan
1501 Posts

Posted - 28 Apr 2014 :  10:40:20 AM  Show Profile  Reply with Quote
I wonder how well the modules are made these days? Maybe from China?
Did you try replacing with a known good module and pick up?.


71' GTO Original 400 M20 3.23 posi
13.95@102.1 MPH on street tires
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Bill Boyle
Horse Feathers (Charter Member)

USA
4793 Posts

Posted - 28 Apr 2014 :  10:56:16 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Drake, I'm waiting to hear back from the owner on it. The tests are done without the module in play. That's a separate test. What I'm describing it purely mechanical except for the pick up coil which fires the strobe on my machine. That might be the culprit, but don't know if it's USA made or something "foreign."

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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Bill Boyle
Horse Feathers (Charter Member)

USA
4793 Posts

Posted - 29 Apr 2014 :  07:54:22 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Well as it turned out, it was "operator error" more or less. But before I get to that--

I verified the HEI pick up was correct for this Pontiac HEI. Meaning it was a Pontiac piece, not a Chevrolet. Then, a test was conducted with a multimeter that determined the part was good. That, eliminated everything but, me, and the Sun machine.

On to the operator error-

So, I went through my set-up procedure and discovered a slight bit of grease or oil that accumulated over the years in the chuck. The oil apparently came from the slight bit of oil inside the housing of the shaft and gear. Many times distributors are pulled from working engines and appear clean but when sitting nearly straight up, gravity makes them ooze. Something I never noticed. Enough oily residue had built up over a 12+ years of curving and prevented a positive grip on the gear. Once the chuck was cleaned with a Q-tip, the drifting issue was solved.


I give credit to two people. First to my son Brian who said, "Dad, are you sure the gear is properly clamped" to which I inaccurately said, "of course." Then to fellow distributor and Pontiac enthusiast Rocky Rotella for suggesting the same thing in an email.

When the pick-up was proven to be good, all that was left was me and/or the machine.


"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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Phil
The Great White Buffalo

USA
7214 Posts

Posted - 10 May 2014 :  1:35:20 PM  Show Profile  Reply with Quote
Interesting.

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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